Image processing apparatus, image processing method, and inkjet printing apparatus

ABSTRACT

For a multi-pass printing, an image of a unit area is printed by M printing scans of M print regions of first and second nozzle arrays. Each of N pieces of column data is printed by a different printing scan. Ejection data for the first nozzle array is generated using a first mask pattern and ejection data for the second nozzle array is generated using a second mask pattern different from the first mask pattern, for each of the N pieces of column data. On that basis, the first mask pattern and the second mask pattern have a complementary relationship in each of the M print regions. Further, in each of the first mask pattern and the second mask pattern, a combination of print regions, of the M print regions, for printing dots at the same position on the print medium has a mutually complementary relationship.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to image processing for inkjet printingapparatuses that print an images by forming dots on a print medium.

Description of the Related Art

For serial inkjet printing apparatuses, variation in ejectioncharacteristics of each nozzle may be recognized as the unevenness ofdensity on the image. As a measure against such unevenness of density,for example, there is known a multi-pass printing method. In themulti-pass printing, the same image area on a print medium is printed bymultiple printing scans while a conveyance operation is performed by adistance shorter than the print width of the print head between theprinting scans. As a result, a line extending in the main scanningdirection is made up of the array of dots printed with multiple nozzlesalternately, which can reduce the unevenness of density resulting fromthe variation in print characteristics of each nozzle.

Meanwhile, for such multi-pass printing, column thinning can be usedtogether. The column thinning is a method in which pixel rows (columns)aligned in the main scanning direction are classified into, for example,odd columns and even columns, and a printing scan for printing only theodd columns and a printing scan for printing the even columns areperformed alternately. Use of the column thinning makes is possible toincrease the scan speed of the print head while the drive frequency ofeach nozzle is kept constant because the ejection cycle of each nozzlecan be set as the interval of every other columns. As a result, thecolumn thinning makes the printing time shorter than ordinary multi-passprinting. Japanese Patent Laid-Open Nos. 2002-29097 and 2004-1560disclose multi-pass printing methods using column thinning together.

Meanwhile, Japanese Patent Laid-Open No. H10-109442(1998) discloses amethod in which multiple nozzle arrays configured to eject the same kindof ink are prepared, and an image that can be printed by one nozzlearray in one printing scan is shared by multiple nozzle arrays forprinting. Use of the technique disclosed in Japanese Patent Laid-OpenNo. H10-109442(1998) also reduces the unevenness of density resultingfrom the variation in ejection characteristics of each nozzle for thesame reason as for multi-pass printing. In addition, multi-pass printingwith a technique disclosed in Japanese Patent Laid-Open No.H10-109442(1998) further improves the image quality. Further, JapanesePatent No. 6131216 discloses a quantization method for reducing theunevenness of lightness that appears at regular intervals when thetechnique in Japanese Patent Laid-Open No. H10-109442(1998) is used.

As described above, recent serial inkjet printing apparatuses are aimedat reducing the unevenness of density resulting from the variation inprint characteristics of each nozzle by, for example, employing columnthinning and a multi-pass printing method or preparing multiple nozzlearrays capable of ejecting the same kind of ink.

Unfortunately, in the case of performing multi-pass printing and columnthinning using multiple nozzle arrays as in Japanese Patent Laid-OpenNo. H10-109442(1998), print position errors between the nozzle arrays inthe conveyance direction may be a new problem besides the variation inejection characteristics of each nozzle. In the case where such a printposition error is relatively large; even if the technique disclosed inJapanese Patent No. 6131216 is used, images printed with differentnozzle arrays do not complement each other in a preferable condition insome cases, causing recognizable unevenness at regular intervals in theconveyance direction.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above problems. Thus,an object of the present invention is to make it possible for an inkjetprinting apparatus that performs multi-pass printing and column thinningusing multiple nozzle arrays configured to eject ink of the same color,to print uniform images without unevenness even if a print positionerror occurs between the nozzle arrays.

According to a first aspect of the present invention, there is providedan image processing apparatus generating ejection data for printing animage in a unit area of the print medium by repeating a printing scanand a conveyance operation alternately, the printing scan being anoperation of using a first nozzle array and a second nozzle array eachhaving a predetermined number of nozzles arrayed in a predetermineddirection, each nozzle configured to eject the same kind of ink, andscanning the first nozzle array and the second nozzle array in adirection intersecting the predetermined direction while causing eachnozzle to eject the ink toward the print medium, the conveyanceoperation being an operation of conveying the print medium by a distancecorresponding to each of M print regions obtained by dividing thepredetermined number of the nozzles into M regions, M being an integerof four or more, in a direction intersecting the direction of theprinting scan, the image in the unit area of the print medium beingprinted by M printing scans, wherein each of N pieces of column dataobtained by thinning binary dot data in every N-th column, N being aninteger between four and M inclusive, is printed by a different scan ofthe printing scan, the image processing apparatus comprising an ejectiondata generation unit that generates ejection data for the first nozzlearray for each of the N pieces of column data using a first mask patternthat defines, in advance, print-permitted pixels at which dot-printingis permitted and print-not-permitted pixels at which dot-printing is notpermitted, and generates ejection data for the second nozzle array foreach of the N pieces of column data using a second mask patterndifferent from the first mask pattern, wherein (i) the first maskpattern and the second mask pattern have a complementary relationship ineach of the M print regions, and (ii) in each of the first mask patternand the second mask pattern, a combination of print regions, of the Mprint regions, for printing dots at the same position on the printmedium has a mutually complementary relationship.

According to a second aspect of the present invention, there is providedan image processing method of generating ejection data for printing animage in a unit area of the print medium by repeating a printing scanand a conveyance operation alternately, the printing scan being anoperation of using a first nozzle array and a second nozzle array eachhaving a predetermined number of nozzles arrayed in a predetermineddirection, each nozzle configured to eject the same kind of ink, andscanning the first nozzle array and the second nozzle array in adirection intersecting the predetermined direction while causing eachnozzle to eject the ink toward the print medium, the conveyanceoperation being an operation of conveying the print medium by a distancecorresponding to each of M print regions obtained by dividing thepredetermined number of the nozzles into M regions, M being an integerof four or more, in a direction intersecting the direction of theprinting scan, the image in the unit area of the print medium beingprinted by M printing scans wherein each of N pieces of column dataobtained by thinning binary dot data in every N-th column, N being aninteger between four and M inclusive, is printed by a different scan ofthe printing scan, the image processing method comprising an ejectiondata generation step of generating ejection data for the first nozzlearray for each of the N pieces of column data using a first mask patternthat defines, in advance, print-permitted pixels at which dot-printingis permitted and print-not-permitted pixels at which dot-printing is notpermitted, and generating ejection data for the second nozzle array foreach of the N pieces of column data using a second mask patterndifferent from the first mask pattern, wherein (i) the first maskpattern and the second mask pattern have a complementary relationship ineach of the M print regions, and (ii) in each of the first mask patternand the second mask pattern, a combination of print regions, of the Mprint regions, for printing dots at the same position on the printmedium has a mutually complementary relationship.

According to a third aspect of the present invention, there is providedan An inkjet printing apparatus comprising: a first nozzle array and asecond nozzle array each having a predetermined number of nozzlesarrayed in a predetermined direction, each nozzle configured to ejectthe same kind of ink; a print unit that causes the first nozzle arrayand the second nozzle array to perform a printing scan in a directionintersecting the predetermined direction while causing each nozzle toeject the ink toward a print medium; and a conveyance unit that conveysthe print medium by a distance corresponding to each of M print regionsobtained by dividing the predetermined number of the nozzles into Mregions, M being an integer of four or more, in a conveyance directionintersecting the direction of the printing scan, wherein an image in aunit area of the print medium is printed by the M printing scans, whenthe printing scan and a conveyance operation by the conveyance unit arerepeated alternately, and each of N pieces of column data obtained bythinning binary dot data in every N-th column, N being an integerbetween four and M inclusive, is printed by a different scan of theprinting scan, the inkjet printing apparatus further comprising anejection data generation unit that generates ejection data for the firstnozzle array for each of the N pieces of column data using a first maskpattern that defines, in advance, print-permitted pixels at whichdot-printing is permitted and print-not-permitted pixels at whichdot-printing is not permitted, and generates ejection data for thesecond nozzle array for each of the N pieces of column data using asecond mask pattern different from the first mask pattern, wherein (i)the first mask pattern and the second mask pattern have a complementaryrelationship in each of the M print regions, and, (ii) in each of thefirst mask pattern and the second mask pattern, a combination of printregions, of the M print regions, for printing dots at the same positionon the print medium has a mutually complementary relationship.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams illustrating the configuration of theprinting part of a color inkjet printing apparatus;

FIG. 2 is a block diagram illustrating the configuration of control inthe inkjet printing apparatus;

FIG. 3 is a block diagram for explaining a conversion step of imagedata;

FIGS. 4A and 4B are diagrams illustrating an example of dot-arrangementpatterns and the states of printed dots;

FIG. 5 is a diagram for explaining mask patterns and the print states;

FIG. 6 is a diagram illustrating an example of mask patterns for twonozzle arrays and the print states;

FIG. 7 is a diagram illustrating an image printed when the printpositions of the nozzle arrays have a positional error;

FIG. 8 is a diagram illustrating an image printed when the printpositions of the nozzle arrays have a positional error;

FIG. 9A illustrates a dot pattern, and FIG. 9B is a diagram illustratingthe state where the dot pattern is divided and distributed to fourcolumns;

FIGS. 10A and 10B are diagrams illustrating the results of logical ANDoperations performed between column data and mask patterns;

FIGS. 11A and 11B are diagrams illustrating an example ofdot-arrangement patterns and the states of printed dots;

FIG. 12A illustrates a dot pattern, and FIG. 12B is a diagramillustrating the state where the dot pattern is divided and distributedto four columns;

FIGS. 13A and 13B are diagrams illustrating the results of logical ANDoperations performed between column data and mask patterns;

FIGS. 14A and 14B are diagrams illustrating the results of logical ANDoperations performed between column data and mask patterns;

FIG. 15 is a diagram illustrating dot-arrangement patterns of a thirdembodiment;

FIG. 16A illustrates a dot pattern, and FIG. 16B is a diagramillustrating the state where the dot pattern is divided and distributedto four columns; and

FIGS. 17A and 17B are diagrams illustrating the results of logical ANDoperations performed between column data and mask patterns.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

FIGS. 1A and 1B are diagrams illustrating the configuration of aprinting part of a color inkjet printing apparatus 1 applicable to thepresent invention. FIG. 1A is a perspective view of the printing part,and FIG. 1B is an arrangement structure diagram of nozzles 202 on aprint head 201.

As illustrated in FIG. 1A, a print medium S is held between two pairs ofrollers, which are a pair of feed rollers 105 and a pair of rollersformed by a conveyance roller 104 and an auxiliary roller 103, and iskept flat and smooth. The pair of feed rollers 105 and the conveyanceroller 104 rotate while supporting the print medium S to convey it inthe Y direction.

Between these two pairs of rollers is disposed a carriage 106 capable ofreciprocating in the X direction, and on the carriage 106 are mountedink tanks 205 and the print head 201. The ink tanks 205, containing fourcolors of inks (black K, cyan C, magenta M, and yellow Y) separately,are connected to the print head 201 in the state of being mounted on thecarriage 106 and supply these inks to the print head 201.

As illustrated in FIG. 1B, the print head 201 has eight rows of nozzlearrays, every two rows corresponding to each of the four inks, and ineach row, 1280 nozzles are aligned at a pitch of 1200 dpi in the Ydirection. Each nozzle 202 ejects approximately 4 pl of ink toward theprint medium S according to ejection data.

In this embodiment, the nozzle arrays are arranged in the order ofblack, cyan, magenta, yellow, yellow, magenta, cyan, and black from theleft. With this order, the application order of the inks is the same onthe print medium between during printing scans in the forward direction(+X direction) and during printing scans in the backward direction (−Xdirection), reducing color unevenness resulting from the applicationorder of the inks. Note that, this embodiment is not limited to thenumber of nozzle arrays and the order of the arrangement describedabove. There only needs to be two or more rows of nozzle arrays thathave a certain number of nozzles in a certain direction and eject thesame kind of ink.

With the configuration described above, while the carriage 106 isscanning in the forward direction or the backward direction at a certainspeed, the print head 201 ejects ink according to the ejection data, sothat one band of an image is printed on the print medium S. Byintermittently repeating the printing scan (relative scanning) for oneband as described above and a conveyance operation of the print medium Sin the direction intersecting the direction of the printing scan, theimage is gradually formed on the print medium S.

While waiting for a print command, or during a maintenance process ofthe print head 201, the carriage 106 is positioned and waits at the homeposition h indicated by the dotted lines in the figure. Note that in theabove example, the ink tanks 205 and the print head 201 can beindividually detached from the carriage 106; however, the ink tanks 205and the print head 201 may be integrated as a cartridge.

FIG. 2 is a block diagram illustrating the configuration of control inthe inkjet printing apparatus 1. A print control unit 500 mainlyincludes a CPU501 that serves as a calculation unit and a memory 502 andcontrols the entire apparatus according to various programs andparameters stored in the memory 502. The memory 502 also stores maskpatterns and dot-arrangement patterns for performing the characteristicprocess of the present invention.

A conveyance motor driver 403 drives a conveyance motor 401 for rotatingthe conveyance roller 104 and the feed rollers 105 under instructionsfrom the print control unit 500. A carriage motor driver 404 drives acarriage motor 402 for moving the carriage 106 under instructions fromthe print control unit 500. A head driver 405 drives the print head 201to make it perform ejection operation under instructions from the printcontrol unit 500.

For example, the print control unit 500 performs a specified imageprocessing on image data received from a host PC 1200 via an interface400, according to a program stored in the memory 502. With this process,the ejection data (dot data) that can be printed by the print head 201is generated. Then, the print control unit 500 sequentially calls theejection data temporarily stored, based on a program stored in thememory 502 while driving the various drivers to execute printing.

FIG. 3 is a block diagram for explaining a conversion step for imagedata executed by each of the host apparatus 1200 and the printingapparatus 1. The programs running on the operating system of the hostapparatus 1200 include applications and printer drivers. In thisexample, it is assumed that the application J0001 generates 8-bit RGBdata having a resolution of 600 ppi. When a print job occurs, 600 ppi8-bit RGB data generated by the application J0001 is provided to theprinter driver.

The printer driver in this embodiment executes, as its process, afront-end process J0002, back-end process J0003, γ correction processJ0004, halftoning J0005, and print data creation process J0006.Hereinafter, each process will be briefly described.

The front-end process J0002 performs mapping of the color gamut (Gamut).In other words, data conversion is performed to map the color gamutreproducible by RGB data conforming to sRGB standard, received by theapplication J0001, within the color gamut reproducible by the printingapparatus 1. Specifically, a three-dimensional look-up table (LUT) isused to convert 8-bit RGB data into 8-bit R′G′B′ data having differentcontents.

The back-end process J0003 performs data conversion so that the colorsrepresented by the 8-bit R′G′B′ data outputted from the front-endprocess J0002 can be expressed by the ink colors (cyan C, magenta M,yellow Y, and black K) used in the printing apparatus. Specifically, athree-dimensional LUT is used to convert the 8-bit R′G′B′ data into8-bit CMYK data.

Note that the look-up tables used in the front-end process J0002 and theback-end process J0003 do not need to have output signal values preparedfor all the combinations of input signal values. Only the relationshipsbetween input signals and output signals at specified lattice points maybe stored, and for input signal values other than those of the latticepoints, the output signal values may be calculated also usinginterpolation operations.

The γ correction process J0004 performs a correction process so that theimage density expressed on the print medium has linearity to the inputsignal (tone signal). Specifically, by referring to a one-dimensionallook-up table prepared for each ink color, the γ correction processJ0004 converts 8-bit data (CMYK) for each ink color into 8-bit data(C′M′Y′K′) for each of the same ink colors. The processes after the γcorrection process J0004, explained below, are performed individuallyfor each ink color.

The halftoning J0005 performs a quantization process of converting 8-bitdata representing 256 tones into 4-bit data representing 9 tones.Although this embodiment uses multi-level error diffusion processing, adither method or the like may be used for this process. This 4-bit dataserves as indexes for indicating the dot-arrangement patterns at adot-arrangement patterning process J0007 described later.

In the print data creation process J0006, the 4-bit data for each colorof each pixel at a resolution of 600 ppi, generated through theprocesses described above, is organized for all the pixels included inthe print job, and print data to which print control informationspecifying the printing method is added is created. The print data istransferred to the printing apparatus 1.

When receiving the print data, the print control unit 500 of theprinting apparatus 1 performs the dot-arrangement patterning processJ0007 and a mask data conversion process J0008 in order, based on thecontents of the print data. Data that can be handled by the print head201 in this embodiment is binary data indicating dot-printing (1) or nodot-printing (0) for each of the 1200 dpi pixels. For this reason, thedot-arrangement patterning process J0007 serves as a dot-data generationunit for generating binary dot data by converting 4-bit data indicating9 tones of each of the 600 ppi pixels into binary data of 1200 dpiindicating dot-printing (1) and no dot-printing (0).

FIGS. 4A and 4B are diagrams illustrating examples of dot-arrangementpatterns that the dot-arrangement patterning process J0007 refers to andthe states of dots printed on the print medium, corresponding to thesepatterns. In FIG. 4A, the levels shown on the left indicate tone levelvalues (0 to 8) indicated by 4-bit data of each of the 600 ppi pixels.The patterns of length 2×width 4 shown on the right side of the levelsare dot-arrangement patterns for expressing the tones indicated by thecorresponding levels, by selecting dot-printing or no dot-printing foreach of the 1200 dpi pixels. For level 0, no dot is printed in any areaof the length 2×width 4, and the number of printed dots increases by onefor every level increase.

In the dot-arrangement pattern, each cell corresponds to one of the 1200dpi×1200 dpi pixels, and a set of 2×4 cells corresponds to one of the600 ppi pixels. In this embodiment, the columns (lines) in eachdot-arrangement pattern are called the first column, the second column,the third column, and the fourth column from the leftmost column (line),and the different columns are printed during different printing scans.Then, when dots are actually printed on the print medium, the dots ofthe third column are printed at the same positions as those of the firstcolumn, and the dots of the fourth column are printed at the samepositions as those of the second column. In other words, on the printmedium, the set of the left 2×2 pixels and the set of the right 2×2pixels of the 2×4 pixels are printed with one on top of the other.

FIG. 4B illustrates the states of dots printed with the set of the left2×2 pixels and the set of the right 2×2 pixels overlaid with one on topof the other based on the dot-arrangement patterns illustrated in FIG.4A. The symbol “⊚” represents a pixel at which two dots are printed withone on top of the other, the symbol “∘” represents a pixel at which onedot is printed, and a blank cell represents a pixel at which no dot isprinted.

In this embodiment, as illustrated in FIG. 4A, four dot-arrangementpatterns (4n) to (4n+3) are prepared for each level and used in order inthe main scanning direction and the sub scanning direction. With thissetting, on the print medium, four kinds of dot-printed statesillustrated in FIG. 4B are to be positioned in order in the mainscanning direction and the sub scanning direction. Preparing multipledot-arrangement patterns having different dot layouts for the same levelvalue in this way disperses the ejection frequency of each nozzle,making the image on the print medium smooth, when the image has auniform tone in which the same level value continues.

FIG. 3 is referred to again. The 1200 dpi dot data generated at thedot-arrangement patterning process J0007 is passed to the mask dataconversion process J0008. The mask data conversion process J0008allocates this dot data to multiple printing scans using mask patternsprepared in advance and generates data for each nozzle array to ejectink in each printing scan, and thus, the mask data conversion processJ0008 serves as an ejection data generation unit. Specifically, for eachof the 1200 dpi pixels, the mask data conversion process J0008 performslogical AND operations between 1-bit data received from thedot-arrangement patterning process J0007 and 1-bit data defined by themask pattern to determine the nozzle and printing scan for printing eachpiece of the dot data.

FIG. 5 is a diagram for explaining an example of the mask pattern andthe print state in the case of using the mask pattern. The mask patterndefines print-permitted pixels at which printing is permitted andprint-not-permitted pixels at which printing is not permitted, and inthe figures, the print-permitted pixels are indicated by black, and theprint-not-permitted pixels are indicated by white. Here, description isprovided for the case of performing 4-pass multi-pass printing with2-column thinning.

In the case of 2-column thinning, the print head 201 alternatelyperforms a printing scan for printing odd columns in the dot-arrangementpattern and a printing scan for printing even columns. In the case of4-pass multi-pass printing, the nozzle arrays of the print head areequally divided into four regions, and every time one printing scan ofthe print head is performed, the print medium is conveyed in theconveyance direction by the distance corresponding to each region. Inother words, in the case of performing 4-pass multi-pass printing with2-column thinning, an image in a unit area on the print medium iscompleted by two printing scans for odd columns and two printing scansfor even columns.

The mask pattern for such a case is formed, as illustrated in FIG. 5,such that the first print region and the third print region, which printidentical columns, have a mutually complementary relationship, and thesecond print region and the fourth print region, which print the otheridentical columns, have a mutually complementary relationship. Althoughin FIG. 5, the ratio of print-permitted pixels (print permission rate)of each print region is 50% so that the mutual complementation makes theprint permission rate 100%, the print permission rate of each print areadoes not have to be equal as long as the above 100% complementationrelationship is kept.

The right side of the mask patterns in FIG. 5 illustrates a state wherean image is being formed in a unit area along with printing scans. Here,the illustration is provided for the case where all of the 600 ppipixels are at level 8, and two dots are printed at each of the 1200 dpipixels (see FIGS. 4A and 4B). White indicates pixels with no dotprinted; gray, pixels with one dot printed; and black, pixels with twodots printed. In the memory 502, multiple binary mask patterns eachdefining dot

print-permitted pixels and print-not-permitted pixels as described aboveare stored in advance being associated with print modes and ink colors.The mask data conversion process J0008 reads one piece of the mask datafrom the memory 502 based on information indicated by the print controlinformation and performs logical AND operations between the one piece ofthe mask data and binary dot data generated in the dot-arrangementpatterning process J0007. The 1-bit data thus obtained, which is dotdata to be actually printed in each printing scan, is transmitted to ahead drive circuit J0009.

The head drive circuit J0009 applies drive pulses to the print head 201to cause each nozzle to perform ejection operation according to the1-bit data obtained from the mask data conversion process J0008,

Hereinafter, description will be provided for characteristic maskpatterns of the present invention in detail. To explain generalfunctions of the mask patterns, FIG. 5 illustrates an example in whichthe image in a unit area is printed by 4-pass multi-pass printing of onenozzle array with 2-column thinning. In this embodiment, using twonozzle arrays, the first nozzle array and the second nozzle array, whicheject ink of the same color, 4-pass multi-pass printing with 4-columnthinning is performed.

FIG. 6 is a diagram illustrating mask patterns that can be used in thecase of performing 4-pass multi-pass printing with 4-column thinningusing two nozzle arrays, the first nozzle array and the second nozzlearray, which eject ink of the same color, and also illustrates the printstate in this case. In the case of 4-column thinning, the print headperforms in order, scanning for printing the first column, scanning forprinting the second column, scanning for printing the third column, andscanning for printing the fourth column. In the case of 4-passmulti-pass printing, the nozzle array area of the print head is dividedinto four regions, the first to fourth regions, and every time oneprinting scan of the print head is performed, the print medium isconveyed in the conveyance direction by the distance corresponding toeach print region. In other words, in the case of performing 4-passmulti-pass printing with 4-column thinning, the image in a unit area ofthe print medium is completed by a printing scan for the first column, aprinting scan for the second column, a printing scan for the thirdcolumn, and a printing scan for the fourth column using the first andsecond nozzle arrays.

In this case, the mask patterns used by the first and second nozzlearrays which print the same columns in the same printing scan have acomplementary relationship in each of the first, second, third, andfourth print regions. In other words, the print permission rate of eachprint region is 100%, and thus, one dot is printed at each of all thepixels of the corresponding columns in each printing scan with eitherthe first or second nozzle array. FIG. 6 illustrates, as an example,mask patterns in which print-permitted pixels and print-not-permittedpixels are arranged such that these pixels depict inverted characters(A, B, C, and D), to make it easy to understand the complementaryrelationship.

The right side in FIG. 6 illustrates a state where an image is beingformed in a unit area along with printing scans. The image in the unitarea is completed by the image of every fourth column being printed inorder in four printing scans.

FIG. 7 illustrates an image printed using the mask patterns illustratedin FIG. 6 in the case where the print position of the first nozzle arrayand the print position of the second nozzle array have a positionalerror by the distance corresponding to one pixel in the conveyancedirection. The complementary relationship between the first and secondnozzle arrays is lost in each of the first, second, third, and fourthprint regions, and pixels where dots are printed with both the first andsecond nozzle arrays and pixels where a dot is not printed with eithernozzle array are included mixedly. Then, also in the completed imagecreated by overlaying such four regions on top of each other, the numberof overlaid dots is unbalanced among the pixels along with thepositional error of the mask patterns, degrading the uniformity of theimage.

FIG. 8 is a diagram illustrating a print state in the case of replacingthe mask patterns with characteristic mask patterns of this embodiment,under the same conditions as in FIG. 7. A first condition for formingmask patterns of this embodiment is that mask patterns used by the firstand second nozzle arrays which print the same columns in the sameprinting scan have a complementary relationship in all the print areas.This condition is satisfied also by the mask patterns illustrated inFIGS. 6 and 7. A second condition is that mask patterns have acomplementary relationship in the combination of the first and thirdprint regions which are different columns on the data but are forprinting dots at the same positions on a print medium and in thecombination of the second and fourth print regions which are alsodifferent columns on the data but are for printing dots at the samepositions on the print medium.

Specific description will be provided with reference to FIG. 8. The maskpattern (white hollow character A) of the first print region for thefirst nozzle array has a complementary relationship with the maskpattern (black solid character A) of the first print area for the secondnozzle array (condition 1), and also has a complementary relationshipwith the mask pattern (black solid character A) of the third printregion for the first nozzle array (condition 2). The mask pattern (whitehollow character B) of the second print region for the first nozzlearray has a complementary relationship with the mask pattern (blacksolid character B) of the second print region for the second nozzlearray (condition 1), and also has a complementary relationship with themask pattern (black solid character B) of the fourth print region forthe first nozzle array (condition 2).

In the case of using the mask patterns described above; if a printposition error occurs between the first nozzle array and the secondnozzle array, the complementary relationship between the first nozzlearray and the second nozzle array in each printing scan is lost as inFIG. 7. However, the complementary relationship between the first printregion (white hollow character A) and the third print region (blacksolid character A) for the same unit area is kept, and the complementaryrelationship between the second print region (white hollow character B)and the fourth print region (black solid character B) for the same unitarea is also kept. Consequently, when the four print regions areoverlaid on top of each other, the number of overlaid dots is uniformlytwo for each among all of the 1200 dpi pixels, providing a uniformimage.

In other words, with the mask patterns of this embodiment, acomplementary relationship is satisfied among the four print regions foreach of the first nozzle array and the second nozzle array.Consequently, even if the print positions of the first nozzle array andthe second nozzle array have an error in any direction, an imagesatisfying the complementary relationship is overlaid on an imagesatisfying the complementary relationship, and thus preventingdeterioration of the uniformity of the image.

Note that in the above, the mask patterns have a complementaryrelationship in the combination of the first print region and the thirdprint region and in the combination of the second print region and thefourth print region as a combination for printing dots at the samepositions on the print medium. However, for 4-column thinning, columnscanning does not necessarily have to be performed in order from theleft side of the dot-arrangement pattern. For example, after theprinting scan of the first column, the printing scan of the third columnmay be performed, and then, the printing scans of the second column andthe fourth column may be performed. In this case, a complementaryrelationship is given to the mask patterns in each of the combination ofthe first print region and the second print region and the combinationof the third print region and the fourth print region. In any case, ifthe print regions for printing the first column and the third columnwhich correspond to the same positions on the print medium have acomplementary relationship, and the print regions for printing thesecond column and the fourth column have a complementary relationship,the above effect can be obtained.

However, in the case where multi-pass printing is performed using bothdirections, even the same nozzle array may cause a print position errorin the main scanning direction between in the forward scanning and inthe backward scanning. In this case, even if the mask patterns of theadjoining first and second print regions have a complementaryrelationship; if a positional error occurs in the main scanningdirection between these mask patterns, the mutual complementaryrelationship is lost. Even in this case, for the mask patternsillustrated in FIG. 8, the mask patterns having a complementaryrelationship can be used in the printing scans in the same direction forthe unit area, making less noticeable the influence of the printposition error between the forward and backward directions. In otherwords, use of the mask patterns as illustrated in FIG. 8 makes itpossible to print uniform images in which both the influence of theprint position error between the nozzle arrays and the influence of theprint position error between the forward and backward directions arereduced.

Meanwhile, in the above, the description has been provided for the casewhere all of the 600 ppi pixels are at level 8, and two dots are printedat all of the 1200 dpi pixels. For a case of another level (tone value),use of mask patterns as illustrated in FIG. 8 may not provide a uniformimage. Specific description will be provided below. FIG. 9A illustratesa dot pattern generated using the dot-arrangement patterns illustratedin FIG. 4 in the case where all of the 600 ppi pixels are at level 2,and FIG. 9B illustrates the state where the dot pattern is divided anddistributed to four columns. For example, column 1 illustrated in FIG.9B has columns coming from every fourth column, such as the firstcolumn, the fifth column, the ninth column, and so on, in FIG. 9A, andcolumn 2 has columns coming from every fourth column, such as the secondcolumn, the sixth column, the tenth column, and so on, in FIG. 9A. Eachof the data of column 1, the data of column 2, the data of column 3, andthe data of column 4 illustrated in FIG. 9B is to be printed in the samescanning of the print head.

FIG. 10A illustrates the results of logical AND operations performedbetween each piece of column data illustrated in FIG. 9B and the maskpatterns described with reference to FIG. 8. FIG. 10B illustrates acomparison of the states of images printed by 4-pass multi-pass printingbetween in the case where a print position error occurs between thefirst and second nozzle arrays and in the case where no error occurs.

In the case where no print position error occur between the first nozzlearray and the second nozzle array, the complementary relationshipbetween the first nozzle array and the second nozzle array is kept ineach printing scan, and the image after four printing scans is uniform.However, in the case where a print position error exists between thefirst nozzle array and the second nozzle array, overlaid images by fourprinting scans does not provide a uniform image. This is caused becausethe positions of the two dots in the layout at level 2 are not positionsprinted at the same position on the print medium. This is because sincethe positions of the two dots are not positions printed at the sameposition on the print medium, even if the mask patterns for the firstand third columns for printing dots at the same positions on the printmedium have a complementary relationship, the effect of thecomplementary relationship cannot be obtained.

In light of the situation above, the inventors of the present inventionhas judged that to provide uniform images at any level, it is effectiveto prepare dot-arrangement patterns in which two dots are printed at thesame position as much as possible on a print medium at any level.

FIGS. 11A and 11B are diagrams illustrating dot-arrangement patternsused in this embodiment and the states of printed dots on a printmedium, corresponding to these patterns. For example, referring to level2, two dots are positioned in every other column (such as the first andthird columns) of the same raster (upper row or lower row) so that thetwo dots are printed at the same pixel position on a print medium. Inthis way, in the dot-arrangement patterns in this embodiment, the dotlayout at each level is defined such that as many combinations aspossible of dots that are printed at the same pixel positions in a printmedium are included.

FIG. 12A illustrates a dot pattern generated using the dot-arrangementpatterns in this embodiment illustrated in FIG. 11 in the case where allof the 600 ppi pixels are at level 2, and FIG. 12B illustrates the statewhere the dot pattern is divided and distributed to four columns.

FIG. 13A illustrates the results of logical AND operations performedbetween each piece of column data illustrated in FIG. 12B and the maskpatterns described with reference to FIG. 8. Further, FIG. 13Billustrates a comparison of the states of images printed by 4-passmulti-pass printing according to the dot patterns illustrated in FIG.13A between in the case where a print position error occurs between thefirst and second nozzle arrays and in the case where no error occurs.

As illustrated in FIG. 13B, in the case where no print position erroroccurs, two dots are printed one on top of the other at half of thepixels, and no dot is printed at the other half; in the case where aprint position error occurs, one dot is printed at each of all thepixels. In this way, although there is a difference in the state ofoverlaid dots, both images are uniform, and there is no conspicuoustexture unique to the mask patterns, unlike the case illustrated in FIG.10B where the print position error occurs. In other words, use of thedot-arrangement patterns in this embodiment illustrated in FIG. 11 andmask patterns satisfying the two conditions described using FIG. 8 makesit possible to print uniform images even when a print position erroroccurs between the first nozzle array and the second nozzle array.

In a configuration in which 4-pass multi-pass printing with 4-columnthinning is performed using two nozzle arrays, this embodiment describedabove makes it possible to print uniform images without unevenness evenwhen a print position error occurs between the nozzle arrays.

Second Embodiment

Also in this embodiment, image processing is performed according to theblock diagram illustrated in FIG. 3 using the inkjet printing apparatusillustrated in FIGS. 1 and 2. In this embodiment, using the first nozzlearray and the second nozzle array which eject ink of the same color,8-pass multi-pass printing with 4-column thinning is performed. Thedot-arrangement patterning process J0007 uses the dot-arrangementpatterns illustrated in FIG. 11A. Thus, the dot pattern generated in thecase where all of the 600 ppi pixels are at level 2 and the state wherethe dot pattern is divided and distributed to four columns areillustrated in FIGS. 12A and 12B.

FIG. 14A illustrates mask patterns used in this embodiment and theresults of logical AND operations performed between the mask patternsand each piece of column data illustrated in FIG. 12B. In the case of8-pass multi-pass printing, the nozzle array region of the print head isdivided into eight regions of first to eighth regions, and the printmedium is conveyed in the conveyance direction by the distancecorresponding to an unit area (corresponding to one region) for everyprinting scan. Thus, in the case where 8-pass multi-pass printing with4-column thinning is performed, the image in the unit area on the printmedium is completed by performing two printing scans for each of thefirst column, the second column, the third column, and the fourthcolumn.

Also in this embodiment, mask patterns satisfying the same twoconditions as in the first embodiment are prepared. In other words, themask patterns in this embodiment satisfies the first condition that themask patterns used by the first and second nozzle arrays which print thesame columns in the same printing scan have a complementary relationshipin all of the eight print regions. The mask patterns in this embodimentalso satisfies the second condition that the mask patterns have acomplementary relationship in the combination of the first, third,fifth, and seventh print regions which print dots at the same positionson the print medium and also in the combination of the second, fourth,sixth, and eighth print regions which print dots at the same positionson the print medium.

FIG. 14B illustrates a comparison of the states of images printed by8-pass multi-pass printing according to the dot patterns illustrated inFIG. 14A between in the case where a print position error occurs betweenthe first and second nozzle arrays and in the case where no erroroccurs. As in FIG. 13B described in the first embodiment, the images areuniform in both the case where a print position error occurs and thecase where no error occurs, and there is no conspicuous texture uniqueto the mask patterns, unlike the case illustrated in FIG. 10B where theprint position error occurs. In other words, use of the dot-arrangementpatterns illustrated in FIG. 11 and mask patterns satisfying the abovetwo conditions as illustrated in FIG. 14A makes it possible to printuniform images even when a print position error occurs between the firstnozzle array and the second nozzle array.

Third Embodiment

Also in this embodiment, image processing is performed according to theblock diagram illustrated in FIG. 3 using the inkjet printing apparatusillustrated in FIGS. 1 and 2. Also as in the first embodiment, using thefirst nozzle array and the second nozzle array which eject ink of thesame color, 4-pass multi-pass printing with 4-column thinning isperformed. In this embodiment, the dot-arrangement patterning processJ0007 uses dot-arrangement patterns different from those used in theabove embodiments.

FIG. 15 is a diagram illustrating dot-arrangement patterns used in thisembodiment. In this embodiment, eight dot patterns (8n) to (8n+7) areprepared for each level and used in the main scanning direction inorder. Here, the dot patterns (8n) to (8n+3) are the same as thoseindicated by (4n) to (4n+3) in FIG. 11A. In addition, the dot patterns(8n+4) to (8n+7) are the same as those indicated by (4n) to (4n+3) inFIG. 4A. In other words, the dot-arrangement patterns in this embodimenthave both the characteristics of the dot-arrangement patternsillustrated in FIG. 4A and those of the dot-arrangement patternsillustrated in FIG. 11A.

For the dot-arrangement patterns illustrated in FIG. 11A, a uniformimage can be outputted when a steady print position error occurs, suchas the print position error between the first nozzle array and thesecond nozzle array; however, density unevenness may occur when a suddenconveyance error occurs. Specific description will be provided belowusing FIG. 13.

In the case where neither a sudden conveyance error nor a print positionerror between the first and second nozzle arrays occurs, the whole areaof an image printed by 4-pass multi-pass printing is a uniform imageindicated by “NO POSITION ERROR OCCURS” in FIG. 13B. In the case whereno sudden conveyance error occurs, but a print position error betweenthe first and second nozzle arrays occurs, the whole area of an image isa uniform image indicated by “POSITION ERROR OCCURS” in FIG. 13B.

However, in the case where a sudden conveyance error occurs during4-pass multi-pass printing, the image indicated by “NO POSITION ERROROCCURS” and the image indicated by “POSITION ERROR OCCURS” in FIG. 13Bare mixed in the conveyance direction whether a print position errorbetween the nozzle arrays occurs or not. Since there is a difference inthe coverage factor (area factor) of dots on a print medium betweenthese two images, visual density difference is recognized between them.Specifically, the density of the image having a large area factor,indicated by “POSITION ERROR OCCURS” is perceived to be higher than thatof the image having a small area factor, indicated by “NO POSITION ERROROCCURS”. As a result, the occurrence of a sudden conveyance error causesan abrupt occurrence of a high-density band and a low-density band in auniform image, which are recognized as the unevenness of density. Inparticular, in the state where overlaid dots (⊚) exist among blankpixels as in level 2 of FIG. 11A, a slight positional error between twodots forming the overlaid dots greatly changes the area factor, whichtends to make the unevenness of density conspicuous.

In other words, the dot-arrangement patterns illustrated in FIG. 11Ahave an effect of making inconspicuous a steady print position error,such as a print position error between the nozzle arrays, but does nothave a resistance (robustness) against a sudden print position errorsuch as a conveyance error. On the other hand, in the dot-arrangementpatterns illustrated in FIG. 4A, overlaid dots (⊚) are not generated upto level 2 as illustrated in FIG. 4B, and two dots are separatelypositioned in different rows of the raster (upper row and lower row) inthe layout. For this reason, even when a sudden print position erroroccurs, large variation in the area factor is less likely to occur.

FIG. 16A illustrates a dot pattern generated using the dot-arrangementpatterns in this embodiment illustrated in FIG. 15 in the case where allof the 600 ppi pixels are at level 2, and FIG. 16B illustrates the statewhere the dot pattern is divided and distributed to four columns.

FIG. 17A illustrates the results of logical AND operations performedbetween each piece of the column data illustrated in FIG. 16B and themask patterns described with reference to FIG. 8. Further, FIG. 17Billustrates a comparison of the states of images printed by 4-passmulti-pass printing according to the dot patterns illustrated in FIG.17A between in the case where a print position error occurs between thefirst and second nozzle arrays and in the case where no error occurs.

As illustrated in FIG. 17B, both in the case where a print positionerror occurs and in the case where no error occurs, pixels at which twodots are printed one on top of the other, pixels at which one dot isprinted, and pixels at which no dot is printed are dispersedly mixed,providing a uniform image. In either case, when a sudden conveyanceerror occurs, there are places where overlaid dots become separated,increasing the area factor, but there are also places where neighboringdots that had not been overlaid are now overlaid, decreasing the areafactor. In other words, it can be said that even when a suddenconveyance error occurs, and the image indicated by “NO POSITION ERROROCCURS” and the image indicated by “POSITION ERROR OCCURS” are mixed,the difference in the area factor between these two images is small, andit is difficult to perceive the difference as the unevenness of density.

As has been described above, this embodiment allows for resistanceagainst both types of print position errors by mixing thedot-arrangement patterns robust against print position errors betweenthe nozzle arrays as illustrated in FIG. 15 and the dot-arrangementpatterns robust against sudden conveyance errors.

Note that in FIG. 15, among the dot-arrangement patterns prepared, halfof them are ones robust against print position errors between the nozzlearrays, and the other half are ones robust against sudden conveyanceerrors; however, this ratio may be changed as appropriate. For example,in the case where conveyance errors are more conspicuous on an imagethan print position errors between the nozzle arrays, it is preferablethat five or more of the eight dot-arrangement patterns be thedot-arrangement patterns robust against sudden conveyance errors, andthat the remaining patterns be the dot-arrangement patterns robustagainst print position errors between the nozzle arrays. On the otherhand, in the case where print position errors between the nozzle arraysoccur more often than conveyance errors, it is preferable that five ormore of the eight dot-arrangement patterns be the dot-arrangementpatterns robust against print position errors between the nozzle arrays,and that the remaining patterns be the dot-arrangement patterns robustagainst sudden conveyance errors. It is a matter of course that thenumber of kinds of dot-arrangement pattern prepared in association witheach level is not limited to eight. More patterns may be prepared, or ofthe four kinds of dot-arrangement pattern as in the above embodiments,the dot-arrangement patterns robust against print position errorsbetween the nozzle arrays and the dot-arrangement patterns robustagainst sudden conveyance errors may be mixed. In general, preparing alarger number of dot-arrangement patterns is effective to make theejection frequencies of all the nozzles equal and to disperse variousnoises unique to the printing apparatus.

In the above embodiments, the description has been provided using themask patterns in which print-permitted pixels and print-not-permittedpixels are arranged to show the inverted characters (A, B, C, and D) tomake the effects easy to understand. However, it is a matter of coursethat the present invention is not limited to such mask patterns. Themask patterns satisfying the above first and second conditions can beset in any way without losing the effects of the present invention. Forexample, gradation masks or the like, which are commonly used to improvethe robustness against conveyance errors, may be suitably used.

In addition, although in the above, the description has been provided asexamples for the case of 4-pass or 8-pass multi-pass printing with4-column thinning, the present invention is not limited to this method.Even for N-column thinning, where N is an integer of 4 or more, thepresent invention functions effectively as long as the print areascorresponding to the columns for printing at the same positions on aprint medium have complementary relationships. The methods of the aboveembodiments can be suitably applied to any configurations in whichM-pass multi-pass printing is used where M is a number at least largerthan or equal to the number of columns, each of the nozzle arrays isdivided into M print areas, and a unit area of the print medium isprinted by M printing scans.

Although in the above, the description has been provided as an examplefor the color inkjet printing apparatus illustrated in FIGS. 1A and 1B,the present invention is not limited to this type of printing apparatus.For example, even for inkjet printing apparatuses dedicated tomonochrome printing using only black ink, if the printing apparatusincludes multiple nozzle arrays for ejecting the black ink, the presentinvention functions effectively.

Further, in the above, the description has been provided, with referenceto FIG. 3, for the case where the host apparatus performs the processesup to the halftoning, and the printing apparatus performs the processesfrom the dot-arrangement patterning process. However, the presentinvention is not limited to this method. The printer driver of the hostapparatus may perform the processes up to the mask data conversionprocess and transmit the generated ejection data to the printingapparatus. Alternatively, the printing apparatus may perform all theprocesses from the front-end process. In any case, the apparatus thatuses the characteristic mask patterns of the present invention toperform the mask data conversion process is an image processingapparatus of the present invention.

Another Example

The present invention can be realized by the process in which a programfor implementing one or more functions of the above embodiments isprovided to a system or an apparatus via a network or a storage media,and one or more processors of a computer in the system or the apparatusread and execute the program. The present invention can also be realizedby circuitry that implements one or more functions (for example, anASIC).

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2017-241107 filed Dec. 15, 2017, which is hereby incorporated byreference wherein in its entirety.

What is claimed is:
 1. An image processing apparatus generating ejectiondata for printing an image in a unit area of the print medium byrepeating a printing scan and a conveyance operation alternately, theprinting scan being an operation of using a first nozzle array and asecond nozzle array each having a predetermined number of nozzlesarrayed in a predetermined direction, each nozzle configured to ejectthe same kind of ink, and scanning the first nozzle array and the secondnozzle array in a direction intersecting the predetermined directionwhile causing each nozzle to eject the ink toward the print medium, theconveyance operation being an operation of conveying the print medium bya distance corresponding to each of M print regions obtained by dividingthe predetermined number of the nozzles into M regions, M being aninteger of four or more, in a direction intersecting the direction ofthe printing scan, the image in the unit area of the print medium beingprinted by M printing scans, wherein each of N pieces of column dataobtained by thinning binary dot data in every N-th column, N being aninteger between four and M inclusive, is printed by a different scan ofthe printing scan, the image processing apparatus comprising an ejectiondata generation unit that generates ejection data for the first nozzlearray for each of the N pieces of column data using a first mask patternthat defines, in advance, print-permitted pixels at which dot-printingis permitted and print-not-permitted pixels at which dot-printing is notpermitted, and generates ejection data for the second nozzle array foreach of the N pieces of column data using a second mask patterndifferent from the first mask pattern, wherein (i) the first maskpattern and the second mask pattern have a complementary relationship ineach of the M print regions, and (ii) in each of the first mask patternand the second mask pattern, a combination of print regions, of the Mprint regions, for printing dots at the same position on the printmedium has a mutually complementary relationship.
 2. The imageprocessing apparatus according to claim 1, further comprising a dot-datageneration unit that generates the binary dot data based on multi-levelimage data, wherein the dot-data generation unit determines dot-printingor dot-not-printing for each column, such that dots are printed with oneon top of the other at the same pixel position on the print medium,regardless of tone level of the image data.
 3. The image processingapparatus according to claim 1, further comprising a dot-data generationunit that generates the binary dot data based on multi-level image data,wherein the dot-data generation unit determines dot-printing ordot-not-printing for each column such that an area where dots areprinted with one on top of the other at the same pixel position on theprint medium and an area where dots are separately printed at differentpixel positions on the print medium are appeared, regardless of tonelevel of the image data.
 4. The image processing apparatus according toclaim 1, wherein in the M printing scans, a scan in a forward directionand a scan in a backward direction are performed alternately, and ineach of the first mask pattern and the second mask pattern, acombination of print regions, of the M print regions, for printing dotsat the same position on the print medium in a printing scan in the samedirection has a mutually complementary relationship.
 5. The imageprocessing apparatus according to claim 1, wherein in the first maskpattern and the second mask pattern, each of the M print regions has aprint permission rate of 50%.
 6. The image processing apparatusaccording to claim 1, wherein each of the M and the N is four.
 7. Theimage processing apparatus according to claim 1, wherein the M is eight,and the N is four.
 8. The image processing apparatus according to claim1, further comprising a printing unit that prints an image on the printmedium using the first nozzle array and the second nozzle arrayaccording to the ejection data generated by the ejection data generationunit.
 9. An image processing method of generating ejection data forprinting an image in a unit area of the print medium by repeating aprinting scan and a conveyance operation alternately, the printing scanbeing an operation of using a first nozzle array and a second nozzlearray each having a predetermined number of nozzles arrayed in apredetermined direction, each nozzle configured to eject the same kindof ink, and scanning the first nozzle array and the second nozzle arrayin a direction intersecting the predetermined direction while causingeach nozzle to eject the ink toward the print medium, the conveyanceoperation being an operation of conveying the print medium by a distancecorresponding to each of M print regions obtained by dividing thepredetermined number of the nozzles into M regions, M being an integerof four or more, in a direction intersecting the direction of theprinting scan, the image in the unit area of the print medium beingprinted by M printing scans wherein each of N pieces of column dataobtained by thinning binary dot data in every N-th column, N being aninteger between four and M inclusive, is printed by a different scan ofthe printing scan, the image processing method comprising an ejectiondata generation step of generating ejection data for the first nozzlearray for each of the N pieces of column data using a first mask patternthat defines, in advance, print-permitted pixels at which dot-printingis permitted and print-not-permitted pixels at which dot-printing is notpermitted, and generating ejection data for the second nozzle array foreach of the N pieces of column data using a second mask patterndifferent from the first mask pattern, wherein (i) the first maskpattern and the second mask pattern have a complementary relationship ineach of the M print regions, and (ii) in each of the first mask patternand the second mask pattern, a combination of print regions, of the Mprint regions, for printing dots at the same position on the printmedium has a mutually complementary relationship.
 10. An inkjet printingapparatus comprising: a first nozzle array and a second nozzle arrayeach having a predetermined number of nozzles arrayed in a predetermineddirection, each nozzle configured to eject the same kind of ink; a printunit that causes the first nozzle array and the second nozzle array toperform a printing scan in a direction intersecting the predetermineddirection while causing each nozzle to eject the ink toward a printmedium; and a conveyance unit that conveys the print medium by adistance corresponding to each of M print regions obtained by dividingthe predetermined number of the nozzles into M regions, M being aninteger of four or more, in a conveyance direction intersecting thedirection of the printing scan, wherein an image in a unit area of theprint medium is printed by the M printing scans, when the printing scanand a conveyance operation by the conveyance unit are repeatedalternately, and each of N pieces of column data obtained by thinningbinary dot data in every N-th column, N being an integer between fourand M inclusive, is printed by a different scan of the printing scan,the inkjet printing apparatus further comprising an ejection datageneration unit that generates ejection data for the first nozzle arrayfor each of the N pieces of column data using a first mask pattern thatdefines, in advance, print-permitted pixels at which dot-printing ispermitted and print-not-permitted pixels at which dot-printing is notpermitted, and generates ejection data for the second nozzle array foreach of the N pieces of column data using a second mask patterndifferent from the first mask pattern, wherein (i) the first maskpattern and the second mask pattern have a complementary relationship ineach of the M print regions, and, and (ii) in each of the first maskpattern and the second mask pattern, a combination of print regions, ofthe M print regions, for printing dots at the same position on the printmedium has a mutually complementary relationship.